17 Heb “In his days [= during the time he rules].”
18 Parallelism and context (cf. v. 4) suggest this nuance for the word often translated “be saved.” For this nuance elsewhere see Ps 119:117; Prov 28:18 for the verb (יָשַׁע [yasha’] in the Niphal); and Ps 12:6; Job 5:4, 11 for the related noun (יֶשַׁע, yesha’).
19 It should be noted that this brief oracle of deliverance implies the reunification of Israel and Judah under the future Davidic ruler. Jeremiah has already spoken about this reunification earlier in 3:18 and will have more to say about it in 30:3; 31:27, 31. This same ideal was espoused in the prophecies of Hosea (1:10–11 [2:1–2 ]), Isaiah (11:1–4, 10–12), and Ezekiel (37:15–28) all of which have messianic and eschatological significance.
20 Heb “his name will be called ‘The Lord our righteousness’.” The Hebrew word translated “justice” here is very broad in its usage, and it is hard to catch all the relevant nuances for this word in this context. It is used for “vindication” in legal contexts (see, e.g., Job 6:29), for “deliverance” or “salvation” in exilic contexts (see, e.g., Isa 58:8), and in the sense of ruling, judging with “justice” (see, e.g., Lev 19:15; Isa 32:1). Here it probably sums up the justice that the Lord provides through raising up this ruler as well as the safety, security, and well-being that result (see vv. 5–6a). In the NT this takes on soteriological connotations (see 1 Cor 1:31 in its context).